Phase stability of Sm_0.5Sr_0.5CoO₃ cathodes for on-planar type, single-chamber, solid oxide fuel cells

The stability of Sm_0.5Sr_0.5CoO₃ (SSC) under reduction conditions is investigated to determine whether it can be used as a cathode material in on-planar type, single-chamber, solid oxide fuel cells. The techniques of X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy are used to reveal the reduction mechanism of SSC. Impedance spectroscopy analysis also provides a better understanding of the influence of decomposed SSC phases on cathode performance. Decomposition of SSC occurs on the surface by the formation of dot-shaped SrO, Co(OH)₂ and CoO on top of the reduced SSC layer at 250 °C in 4% H₂O-96% H₂. The SSC perovskite structure is destroyed at 350 °C in pure hydrogen. There is a catastrophic microstructural change in which SSC is completely decomposed to SrO and CoO that cover the surface of Sm₂O₃.